1. Field of the Invention
This invention relates to document feed systems and is particularly concerned with apparatus for moving documents in succession along a document track.
Document tracks are used, for example, in document encoding and sorting machines, in particular in check encoding machines. They are also used for moving mail, bank notes and other thin planar items.
2. Description of the Prior Art
Most document feed systems are liable to malfunction if two or more documents are fed along the track together. Accordingly means are normally provided to detect when more than one document is located in a particular position along the track. For example, it is known in the prior art to provide pneumatic suction along both sides of a track. A single document is attracted to a suction nozzle on only one side of the track, whereas multiple documents are attracted to suction nozzles on both sides of the track. While such a system enables multiple documents to be detected, it is relatively complicated and expensive.
Other known multiple document detection systems include light sensors. Such optical systems are not always satisfactory if the opacity of the documents varies, and in many cases cannot detect multiple documents when the leading edges of the documents are exactly aligned.